The development of cataract as well as peripheral neurological disorders is one of the main disabilities occurring in diabetic subjects. Aldose reductase appears to be strongly involved in the development of both these severe injuries. The long-term objective of the research is the understanding of the molecular mechanisms, at the enzyme level, underlying the formation of sugar cataract. In particular, the aim of this project is the assessment of the catalytic properties of aldose reductase from the point of view of its metabolic regulation. On the basis of initial lines of experimental evidence, suggesting an interconversion between two forms of the enzyme, induced by oxygen radicals, it is intended to verify the metabolic relationship of the interconversion of aldose reductase with the redox state of the enzyme environment, and evaluate the involvement of the enzyme modification in physiological and/or pathological states of the lens. The study will be accomplished by assessing the possibility of modulation of the enzyme activity by metabolic effectors. To achieve this goal the different enzyme forms will be isolated by classical methods and characterized both for structural and kinetic properties. The conditions leading to the enzyme interconversion in vitro will be defined by using different oxygen radical generation systems, and different radical scavengers. The nature of the protein modification, leading to differences in the catalytic and regulatory properties of aldose reductase, will be investigated. The difference in susceptibility to inhibition observed at different degree of purification of the enzyme and with different substrates will be related to the existence of the two enzyme forms and to possible specific interactions with other macromolecules of the lens. The knowledge of the mechanisms underlying the modulation of aldose reductase will be advantageous in defining strategies for the therapeutic control of the enzyme activity.